Titanium vs other metals

According to this study http://deepblue.lib.umich.edu/bitstream/2027.42/7945/5/bad3274.0005.001.pdfdone by the Engineering Research Institute at the University of Michigan, the notch sensitivity of grade 4 titanium is the same (or very close) to that of steel. I couldn't find anything that specifically discussed grade 2, or 5, which is what most of our parts are made of. But absent some justification otherwise I think this may just be another rumor ascribed to titanium that turns out to not be true.

 

That would explain why a google search using the string 'titanium notch sensitivity' turns up a ton of references, then. It's just a rumour.

I spend a lot of time on a machining forum where this issue has come up on a number of occasions - after failure usually.

If you want to claim that the Ti that you guys sell isn't notch sensitive, OK, I hope you're giving a warranty against failure.

But do NOT make the blanket statement that Ti isn't notch sensitive and do not be so rude as to say 'bull' when there are an absolute *ton* of scientific & engineering papers out there saying the contrary for at least some of the alloys.

Since I'm not at all interested in getting into a pissing contest with a salesman WRT something he's selling, you can have the last word.

PDW

 

PDW,

At what point did I attack you about this? If you thought I was, then I apologize that was not my intent.

And I did a number of searches on google to investigate notch sensitivity in titanium. I became a salesman for it about 3 days ago and I do not consider myself an expert on it, and to my knowledge there is nothing published or stated by Allied Titanium about notch sensitivity.

What I did find was a number of references to foamed titanium casings, and atypical structures being used in medical implants that seem to raise some concerns, but that is not close to the same application as in structual or marine applications.

The question you raise about titanium though is a reasonable one, but the test is not wether titanium suffers from notch sensitivity, but wether it is better or worse in this regard than steel or aluminium. Since neither steel or aluminium are used in medical implants due to bio-incompatibility, the medical studies didn't compare it, they just pointed out a potential problem in titanium without reference to how it compares to other metals.

That is why I found the study by UM to be interesting, because it directly compared titanium to structual steel, and found it to have comperabe notch sensitivity. Does this mean it isn't a problem with either of them? No not at all, but it does mean that the same designes that work with steel will work with titanium, namely not designing notches in things.

 

PDwiley,

Stumble wasn't the rude guy, that was me. I'm going to have to look up grade 2, 4, and 5 since that is not what we use or we don't call it that. May have to eat my words, since you seem to have some data. What kind of steel was used for comparison? Everything? Could be different alloys and heat treats.

BTW, the link you provided returned an 'invalid reference" when I tried to see the paper.

Marc

 

Sorry about the broken link. Try this one. http://deepblue.lib.umich.edu/bitstream/2027.42/7945/5/bad3274.0005.001.pdf

The relavent quote is on page 3 (pg 5 of the PDF) In conclusions.

Upchurch,

Our primary marine grade is Grade 5. Grade 5, also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4, is the most commonly used alloy. It has a chemical composition of 6% aluminium, 4% vanadium, 0.25% (maximum) iron, 0.2% (maximum) oxygen, and the remainder titanium.

Grade 2 and 9 are also commonly used, though much less frequently.

Grade 2 is max of .1% carbon, max .3% iron, Max .015% helium, max .03 nitrogen, max .25% oxygen, minimum 99.2% titanium.
Grade 9 contains 3.0% aluminium and 2.5% vanadium

 

PdWiley,

I searched for "ti notch sensitivity" and there are a lot of references. From what I saw the comments for notch sensitivity were for commercially pure Ti - generally for bio-medical uses. That's not my experience so I accept your statement, but 60% of all Ti is Grade 5 according to Stumbles defination and the articles I read - only 20% is commercially pure (CP). So I still conclude that for our applications there is no issue.

 

Not to knock this thread off it's axis (much), but in reading this thread I think I've now got a use for this stuff!

Now of course I had to go to the website to find out more, saw the intro video, and saw a few parts and such, but not any pricing to make selection and decisions.
http://www.alliedtitanium.com/

I think I finally got a basic concept for my adventure racing proa design and think I could use this in my mast pivoting bolt, and a few other places.
http://youtu.be/I-WoG_pv1ls
I have a lot of pivoting parts in this design and was thinking about SS but could Ti be the better choice?

And how well does TI and Al get along? My beams are going to be Al and the bolts go right thru it.

 

Spin,

Our prices are quoted on demand for most things because of the volatility of the titanium market. However for those things that we sell a lot of (fasteners, tubing, ect.) there are some stock parts available.

If there is something you need I would be more than happy to help you price it out, just drop me a PM so we can work out how I can help you.

As for titanium and aluminium. As I understand it you have about the same problem that you do when titanium and stainless are in contact. The cathode (titanium or stainless) will slowly corrode the aluminium (anode). The solution is to minimize the contact between the two metals and to the extent possible ensure that the anode is larger in size than the cathode. Since the effect of electrolysis is in part governed by the relative size of the two parts.

I am not an engineer, so I can't make statements of sutability for a particular purpose, but titanium has a lot of advantages over stainless, particularly in areas where concerns over corrosion (crevice corrosion particularly) need to be dealt with. In large part because titanium doesn't suffer from corrosion in ambient environments.

 

My company has been having almost all of our underwater stabilization appendages (various incarnations and geometries of wings and foils, with the odd trim tab or interceptor) manufactured exclusively in 6AL4V titanium for about a decade. We found the costs to be only marginally higher than stainless and of course the phys props are are far better so we can engineer much finer foils with the Ti.

Easy to weld, easy to machine, yes. But particularly easy to design with, especially when compared to aluminum, where one must accept huge reduction in allowable stresses where as-welded condition is subject to fully reversing fatigue loads..in salt water. The Ti effectively has no such reductions or limitations to deal with, so in effect, the Ti is far, far stronger than aluminum (about 10x stronger) for certain high-fatigue underwater applications like ours.

And its so pretty!..

 

The SR-71 Blackbird was built using mostly Titanium which at the time we bought from the Russians, our only supplier. We told them we made cooking appliances out of it then we built the fastest airplane in the world out of it and spyed on them with it. They shipped us untold tons of ore for years. Titanium alloy must have a very high melting point because the Blackbird at full speed and altitude is not black but red/ orange as it's skin reaches over 2,000*

 

Rasor,

Ti has a very high melting point of about 3,000F depending on the alloy.

The concern I would have is oxygen embrittlement that can occur at tempratures around 800F. Of course at the altitudes the SR-71 flies that may not be a problem. They may also have been using an alloy that is not sensitive to oxygen in the same way. I don't have any idea, but it would be interesting to know.

 

This is a company that has a lot of experience in design and manufacture of yacht parts from Titanium:

http://www.defi.org.uk/xcontact.html

They design parts in all kinds of materials but titanium is a speciality. They did used to have an in-house facility for manufacture of titanium parts, I am not sure that still exists but I am sure Robert Weguelin will be able to find a way to get your custom parts made as well as designed.

 

Stumble, thanks for the heat info on titanium. Who knows what the Lockheed metal brains came up with for the recipe for the titanium used on the SR-71. I'm sure it was not the standards your company uses for making parts.

 

John,

Allied titanium is in the same business. Though in addition to marine parts we also have a catalog of over 40,000 parts. Quite littlerly everything from anchors to titanium guitar picks. We do not do design work, but do have a number of engineers we can refer to if someone needs a part designed as well.

 

As I see it the point of the thread was to raise awareness of the use Titanium for yachts. As I see it now there is a lot more positive report than negative on it application on marine vessels.
It was not that long ago that people thought 316 was to expensive, now you don't find the lower grades easily any more in stores. I believe this to be a maintenance issue before anything else.
When comparing to Aluminium maintenance and treatment of Aluminium has to be considered in costing. It seems unlikely to get a successful paint job on Alloy now days with the current compliant paints, it's certainly not a one coat application.